Above you see the result of a poll commissioned by the Sun newspaper in Britain.
The Guardian immediately brings in a Muslim, Miqdaad Versi, assistant secretary general of the Muslim Council of Britain, to try and spin this away.

...between 20% and 40% of Northern Irish respondents reported some “sympathy” for violent loyalism or republicanism in the Northern Ireland Life and Times Survey 2007. In essence, Muslims and non-Muslims answer these questions in a similar way.

...
A 2006 ICM poll for the Daily Telegraph found that 20% of British Muslims had sympathy with the “feelings and motives” of the 7/7 bombers, but only 1% (not meaningfully different from 0%) thought that what they did was right. Similarly, conditional support for terrorism was expressed by between 2% (also not meaningfully different from 0%) and 22% of Muslims, depending on the question asked. What this means is that the answer you get depends on the question you ask.

With a Muslim population probably hovering around 4 million give or take, 1% is 40,000 and 2% is 80,000. Either figure is larger than the estimate size of the Islamic State army in Syria. But according to Miqdaad, it's nothing to worry about. Tiny minority of extremists...

The only reasonable point Miqdaad makes is this:

In this case, the poll conducted by Survation does not actually ask whether people have sympathy for Isis or jihadis; it asks whether they have sympathy for those fighting in Syria. This makes a considerable difference as there are many rebel groups fighting against President Assad, some of whom even have the support of western governments.